Assembly line...both for prepping and painting.
For prepping, I'll do a whole unit at a time, clean them up, wash them, base them, then prime them, then put them in the Army Case. Then I'll move on to the next unit and repeat.
I add all the details (sand, rocks, other stuff) to the base before priming, rather than after. Foliage, grass, etc. is added just before I use sealer.
For painting, I just open the case and pick about five of the next figs in queue. I paint the same area on every fig, then go back and start on a new area. Rinse, wash, repeat.
For me, the worst part is prepping: filing, sanding, scraping, filling, etc. is pure tedium to me.